Study of Technology for Preparing Titanium Carbide and Calcium Metal from Perovskite Concentrate by a Carbothermal Method

Substantiation of using a carbothermal method for processing flotation perovskite concentrate is presented. Results of X-ray structural studies of compacted specimens after two sintering stages are provided. It is shown that titanium carbide is formed in the first stage, and in the second stage calcium carbide is formed followed by dissociation into calcium metal and graphite. A dependence is obtained for the degree of transformation of titanium carbide on isothermal exposure duration and excess carbon in the initial charge. Dependence of degree of calcium extraction on isothermal exposure duration is demonstrated. It is shown that the temperature for the beginning of calcium carbidization at a given pressure is ≈ 1600°C. It is established that briquette compaction pressure has almost no effect on calcium extraction, while it affects briquette mechanical strength.

Thermodynamic calculations of equilibrium compositions of phases in contact involved in production processes are performed using HSC Chemistry application software. Results of differential-thermal and thermogravimetric analyses of a charge of a given composition of flotation perovskite and soot are analyzed. In order to study kinetic regularities, correlation coefficients of isothermal exposure duration and reaction rate constant are calculated using kinetic equations of Yander, Gistling–Brownstein, Zhuravlev–Lesokhin–Tempel’man, anti-Gistling, anti-Yander, and Tamman. Apparent activation energy for the first stage of the carbothermal process is calculated using a specific model taking account of results of experiments conducted at different temperatures (Ea = 311.48 kJ/mol). It is established that the dependence obtained for the degree of transformation on isothermal exposure duration is most adequately described by an anti-Yander model formal kinetics equation. Optimum production conditions are selected for the process on the basis of research results: briquette pressing pressure is 8.57 MPa; first stage temperature 1500°C and 1750°C in the second stage; heating rate 17°C/min and 9°C/min respectively. In this case exposure time is 120 min and 60 min in the first and second stages, and residual pressure is 50 Pa and 13.3·10^–3 Pa respectively.